One of the challences for future scientists might be to contact and motivate a prophet
in a past century to create a work of prophecy that can be used as proof for the existence
of time travel. How would future scientists go about in motivating a prophet
to create such a work?

People are motivation driven. Without the right incentive a prophet might not care to colaborate,
the prophecy might get lost and not prove anything.
Communicating with the past seem to be message based. All that can be send must be inside
the communication. Motivation and reward must somehow be found inside the message.

Further to convincing the prophet, the message must preserve its value throughout the centuries
in order not to disappear. What kind of value could be added to a message that makes it stand out?
Hereunder are a number of ideas that would make a message more interesting.

The scientists need to be able to proof beyond doubt that the book of prophecy has been
created by their time travel experiment.
If the scientists cannot prove that the results received back could only have been
generated by their experiment then the theory of communicating with the past cannot be confirmed.
Why would it be so difficult to proof? Well, If a message goes to the 18th century,
then the response would exist for hundreds of years before the experiment.
The contents would be known in detail for all that time.

If it would be possible to hack the secret code inside the message and re-engineer
the original content, message and experiment then the future scientists cannot prove that
the book of prophecy is the results of their own time travel experiment.

It seems that the vision needs to be coded in such a way that only the original
experiment can undoubtedly prove that it is the foundation for the prophets book.

Since a book of prophecy is not necessary a perfect copy of the original message,
but the prophet's interpretation of it, it might be hard or even impossible to link it back
as result of an experiment.